Somebody correct me if I am wrong but, ECU's are just like EMS. (Engine Management Systems). They are what makes everything work in your car. They can control how much air your intake takes in, air conditioner, etc. They cost around 2000 for good ones. You must purchase one if you are going to tune your car. When you have alot of performance done to your car, you would want to get one to control everything. Performance chips gives you around 20-30 hp and gets you better gas milage. You can find very cheap ones at ebay. ($10 ish)
